int sensorValue;

void setup() {
  pinMode(9, OUTPUT);
}

void loop() {
  sensorValue = analogRead(A0);

  if (sensorValue <= 300) {
    digitalWrite(9, LOW);
  }
  else if (sensorValue <= 700) {
    digitalWrite(9, HIGH);
    delay(500);
    digitalWrite(9, LOW);
    delay(500);
  }
  else {
    digitalWrite(9, HIGH);
  }
}